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Warpage Characterization and Improvements for IC Packages with Coreless Substrate

Keywords: Coreless, FEA, Warpage

Coreless package substrates are preferred for their superior electrical performance and thin profile compare to the conventional substrates with core. However, one of the major concerns with the coreless substrate packages is the warpage control. It is difficult to meet the industry standards for co-planarity needs because of the high CTE of the coreless substrates and the missing stiff core material in the stack up of the coreless structure. Finite element analysis (FEA) is utilized to investigate the use of coreless substrate in different package configurations. In this study, known stiffening structures such as a stiffener ring, one or two piece lid and molding options are investigated to characterize the advantages and disadvantages of using each of these structures to control the warpage in an IC package with coreless substrate. Available shadow moiré data is used for initial correlation of the finite element model and further design changes were carried out to stiffen the structure in the final packaged configuration. It is important to understand and make design considerations accordingly to improve assembly yield. Suggestions are made depend on the FEA findings which would guide the selection of the stiffening structure for a package with coreless substrate.